System and method for generating a high speed estimated position output for a position encoder

ABSTRACT

A system and method for generating output signals for a position encoder is provided. The system produces an approximated position signal that is updated at a rate higher than a base rate of the measured transducer position signals. The approximated position signals may be utilized to produce quadrature outputs that are compatible with existing control systems. The measured transducer position signals are processed and/or stored by a signal processing circuit at discrete time intervals. The approximated position values are generated by a high frequency position estimation circuit. The approximated position signal is then compared by an error correction feedback loop to the measured transducer position signal and the resulting difference stored in an error register for use by the error correction feedback loop during the next discrete time interval. In one embodiment, the accuracy of the system may be further improved by utilizing a latch signal to ensure that the approximated position signal and the measured transducer position signal that are compared by the error feedback loop correspond to the same time.

FIELD OF THE INVENTION

[0001] This invention relates generally to position encoders, and moreparticularly to a system and method for the processing of electronicsignals used in position encoders.

BACKGROUND OF THE INVENTION

[0002] Various position encoders for sensing linear, rotary or angularmovement are currently available. These encoders are generally based oneither inductive transducers, capacitive transducers, optical systems,or magnetic scales. In general, an encoder may comprise a transducerwith a readhead and a scale. The readhead may comprise a transducerelement and some transducer electronics. The transducer outputs signalsvary as a function of the position of the readhead relative to the scalealong a measuring axis. The transducer electronics outputs the signalsto a signal processor or processes the signals internally beforeoutputting modified signals indicative of the position of the readheadrelative to the scale. It is also common for an encoder system toinclude an interface electronics separate from the readhead, and tointerpolate or otherwise processes the transducer signals in theinterface electronics before outputting modified signals indicative ofthe position of the readhead relative to the scale to an external hostsystem such as a motion control system or data acquisition system.

[0003] Optical position encoders, both rotary and linear, use opticaldetectors to sense position. The optical elements in some of these typesof encoders have been designed to produce electronic output signals inphase quadrature. In certain types of these systems, an optical readheadoutputs two continuous analog sine wave signals that vary in theamplitude relationship between their phase quadrature signals as theposition changes. The scale pitch λ₀ of an optical scale is thefundamental wavelength of the optical position encoder system. In onecommon type of example optical encoder, the scale pitch λ₀ may be in therange of 20 to 40 micrometers. In such systems the analog quadraturesignals are frequently connected to an electronic signal interpolationdevice. The output of this device is typically two digital quadraturesignals derived from the two continuous analog sine wave signals. Thesedigital quadrature signals are then in a form suitable for use bysubsequent digital processing electronics that determine and/oraccumulate position changes of the optical encoder. In another type oftraditional optical detector, the interpolating electronics may beincorporated inside the readhead.

[0004] In such optical encoder systems the analog signals are producedfrom the optical transducer signals, and the digital signals are createdby the interpolation electronics. The analog sine waves have the scalepitch λ₀ An example of the most simple type of interpolation is commonlyreferred to as 4X interpolation. In this case, the analog quadraturesignals have been changed into digital quadrature waveforms with thesame pitch or wavelength λ₀. The term 4X is used because for eachwavelength traversed, there are 4 edges, or transitions, of the digitalsignals. The subsequent electronics are capable of detecting these 4edges, and thus can detect or record the optical encoder position with aresolution of R1=λ₀/4. As an example of a more advanced type ofinterpolation, the relationship between the analog signals may beinterpolated by an extra factor of 4. In this case, the subsequentelectronics can record the position with a resolution of R2=λ₀/16. Ingeneral, in certain example systems interpolation electronics of thistype have interpolation factors ranging from 4 to 400, or more.

[0005] The nature of the optical systems described above are such thatthe analog waveforms from the position transducer are continuous withposition and time. There are no interruptions in such analog . Becauseof the continuous nature of these signals, the subsequent interpolatingelectronics generally continuously derives and outputs the correspondinginterpolated digital output signals by continuously processing thecontinuous analog waveforms.

[0006] In contrast, U.S. Pat. Nos. 6,005,387, 6,049,204 6,400,138 and6,329,813, each incorporated by reference in their entireties, discloseincremental and absolute inductive position transducers, or encoders,that operate on a sampled basis. In such encoders, the absolute positionis sampled and/or determined on an intermittent or periodic basis, wherethe sample period in some systems is typically in the range of 100-200microseconds or more. At times between the discrete position samples, nonew position information is available. Such “interrupted” or “sampled”signals are not conventional in many motion control systems and are notfamiliar to many users of position encoders. Accordingly, it is not easyfor some users to implement such encoders in various applications. Forexample, in order to be compatible with existing control systems, invarious applications the output from such “position sampling” inductivedevices would preferably be in the form of continuous digital quadraturesignals similar to those of the traditional optical position encoders.However, it is more difficult to create accurate two phase, continuousdigital quadrature signals from the sampled signals of such inductiveencoders and the like than from continuous analog signals, such as thosefrom an optical encoder, or the like.

[0007] The present invention is directed to providing a system andmethod that overcome the foregoing and other disadvantages limiting theuse of position sampled inductive encoders and the like. Morespecifically, the present invention is directed to a system and methodfor generating position outputs at a higher rate than the nativeunderlying sample rate of such position sampled encoders, for example,in the form of continuous incremental quadrature signals.

SUMMARY OF THE INVENTION

[0008] Certain absolute position sensors, for example the inductivetypes disclosed above, operate on an intermittent or periodic samplingbasis. In one example the raw transducer waveforms may be of a threephase type, but the present invention applies equally to a transducerwith any number of phases. The transducer waveforms are sampled and theabsolute position is determined not more frequently than every Tseconds, which is a minimum possible sample period for the device. Theabsolute position that is determined is based on the sampled data.

[0009] Although the transducer electronic system is capable ofdetermining the position intermittently or periodically, in certainimplementations it is desirable to convey position informationexternally in between the intermittent times upon demand from a hostsystem or in a continuous manner between the intermittent times usingindustry standardized incremental quadrature signals or the like. In thecase of continuous incremental quadrature signals, each transition, oredge, of the quadrature signals represents one count up or down, whereone count represents the resolution of the system, or the smallestdetectable incremental position change. As an example system, theresolution in one embodiment could be on the order of fractions of amicrometer, such as 0.1 to 0.5 micrometer. The peak velocity of motionof such a system could be in the range of 5 to 10 meters per second.Given a sampling time T of 100 microseconds, a velocity of 5meters/second, and a resolution of 0.5 micrometer, the total distancetraversed in one period T would be 500 micrometers, or 1000 counts.Therefore, in this example system, it would be desirable for the systemto be outputting incremental quadrature signals at a rate on the orderof 1000 counts/T, or more, and to continue to do so while the systemdetermines the value for the next position sample from the transducer.It would be desirable for this continuous quadrature output to persistduring the time between the transducer position samples, thus bridgingbetween the transducer position samples with estimated positions. Itshould be appreciated that such estimated positions can still bereasonably accurate, because a sampling time T of 100 microseconds, forexample, still provides relative frequent position information relativeto the response frequency of many practical mechanical motion systemsand actuators.

[0010] In accordance with one aspect of the invention, the systemproduces an estimated or approximated position signal that is updated ata rate higher than a base rate of the measured transducer positionsignals. The approximated position signals may be utilized to producequadrature outputs that are compatible with existing control systems.The measured transducer position signals are processed and/or stored bya signal processing circuit at discrete time intervals. The approximatedposition values are generated by a high frequency position estimationcircuit. The approximated position signal is intermittently orperiodically compared by an error correction feedback loop of theposition estimation circuit to an appropriate measured transducerposition signal and the resulting difference stored in an error registerfor use by the position estimation circuit during the next discrete timeinterval. In one embodiment, the accuracy of the approximated positionsignal may be further improved by utilizing a QLATCH signal to ensurethat the approximated position signal and the measured transducerposition signal that are compared by the error feedback loop correspondto the same time. In other words, a timing signal based on the effectivesample time of the measured transducer position signal may be utilizedto generate a QLATCH signal to synchronize the timing for the comparedapproximated position signal.

[0011] In accordance with another aspect of the invention, the systemincludes a position transducer, a transducer signal processing circuit,and a position signal generating circuit. The transducer signalprocessing circuit generates a transducer sample position outputcorresponding to the position of the transducer, according to atransducer sample position output interval that is not less than aminimum transducer sample position output interval. The position signalgenerating circuit generates an approximated position output accordingto an approximated position output cycle interval which is shorter thanthe minimum transducer sample position output interval. The approximatedposition output is incremented by a prescribed increment amount duringthe approximated position output cycle, and the prescribed incrementamount is adjusted when a new transducer sample position output becomesavailable. The adjustment in the prescribed increment amount is based atleast partially on a difference between the approximated position outputand the new transducer sample position.

[0012] In accordance with another aspect of the invention, the variouscomponents of the system may be connected to one another by eitherwireless or wired connections, or a combination thereof. For example,the position transducer, transducer signal processing circuit, andposition signal generating circuit may all be coupled to one another byeither wired or wireless connections.

[0013] In accordance with another aspect of the invention, thedifference determining approximated position output may be selected byeither the transducer signal processing circuit or the position signalgenerating circuit, based on timing information corresponding to thetiming of the new transducer sample position. In one embodiment, thetiming information corresponding to the timing of the new transducersample position may be a value-latching signal output by the transducersignal processing circuit and input by the position signal generatingcircuit. Alternatively, the timing information corresponding to thetiming of the new transducer sample position may either beserially-transmitted timing data or parallel-transmitted timing datathat is output by the transducer signal processing circuit and input bythe position signal generating circuit.

[0014] In accordance with another aspect of the invention, thetransducer sample position output interval that corresponds to a sampletiming of the new transducer sample position may be determined by eitherthe transducer signal processing circuit or the position signalgenerating circuit based on timing information corresponding to thetiming of the difference-determining approximated position output. Thetiming information corresponding to the timing of thedifference-determining approximated position output may be anapproximated position timing signal output by the position signalgenerating circuit and input by the transducer signal processingcircuit.

[0015] In accordance with another aspect of the invention, in oneembodiment the ratio of the nominal approximated position output cycleinterval to the minimum transducer sample position output intervalallows at least 500 approximated position outputs during the minimumpossible transducer sample position output interval. In anotherembodiment, the ratio of the nominal approximated position output cycleinterval to the minimum possible transducer sample position outputinterval allows at least 1800 approximated position outputs during theminimum possible transducer sample position output interval.

[0016] In accordance with another aspect of the invention, the positiontransducer may be an inductive position transducer and the approximatedposition output may comprise a quadrature output. The inductive positiontransducer may be an absolute inductive position transducer. Thetransducer signal processing circuit may be a symmetric samplingtransducer signal processing circuit. The approximated position outputcycle interval may correspond to a maximum quadrature signal frequency,and the maximum quadrature signal frequency may be greater than 500Kilohertz, corresponding to a quadrature counting frequency of 2 millioncounts per second. In another embodiment, the maximum quadrature signalfrequency may be greater than 2.5 megahertz, corresponding to aquadrature counting frequency of 10 million counts per second.

[0017] In accordance with another aspect of the invention, in anotherembodiment the system includes a position transducer and a transducersignal processing circuit. The transducer signal processing circuitgenerates a discrete transducer sample position output corresponding tothe position of the position transducer at a particular time. Thetransducer signal processing circuit generates a timing informationsignal corresponding to the particular time. The transducer sampleposition output and the corresponding timing information signalcorrespond to the particular time and are outputtable to a positiongenerating circuit.

[0018] In accordance with another aspect of the invention, thecorresponding timing information signal that corresponds to theparticular time may be a signal usable to operate a value-latchingcircuit, or a serially-transmitted timing data signal, or aparallel-transmitted timing data signal. In another embodiment, thecorresponding timing information signal that corresponds to theparticular time is output at a time which is not the particular time.

[0019] In accordance with another aspect of the invention, the systemmay include an approximated position generating circuit that generatesan approximated position output according to a nominal approximatedposition output cycle interval which is shorter than a minimumtransducer sample position output interval of the position transducer.The transducer signal processing circuit may output the generateddiscrete transducer sample position output corresponding to the positionof the position transducer at a particular time and the generated timinginformation signal corresponding to the particular time to theapproximated position generating circuit. The approximated positiongenerating circuit may generate a first plurality of approximatedposition outputs that are incremented at a first rate prior to receivingone of the generated discrete transducer sample position outputscorresponding to the position of the position transducer at a particulartime and the generated timing information signal corresponding to theparticular time. The approximated position generating circuit maygenerate a second plurality of approximated position outputs that areincremented at a second rate after receiving the one of the generateddiscrete transducer sample position outputs corresponding to theposition of the position transducer at a particular time and thegenerated timing information signal corresponding to the particulartime. The second rate may be based at least partially on the generateddiscrete transducer sample position outputs corresponding to theposition of the position transducer at a particular time, or thegenerated timing information signal corresponding to the particulartime, or an approximated position output corresponding to the particulartime.

[0020] In accordance with another aspect of the invention, the positiongenerating circuit may be remotely located from the transducer signalprocessing circuit. In one embodiment, the various components of thesystem may be coupled through either a wireless communication interfacecircuit or a wired connection.

[0021] In accordance with another aspect of the invention, the positiongenerating circuit includes at least a portion of one of the followingtypes of circuits: a special-purpose custom digital circuit; aprogrammed commercial gate array; a programmed commercial digital signalprocessing circuit; a programmed general-purpose computer; a programmedmotion-controller; a general-purpose computer; or a programmed computerused as a motion control system host.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The foregoing aspects and many of the attendant advantages ofthis invention will become more readily appreciated as the same becomebetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

[0023]FIG. 1 is a block diagram of a position encoder system;

[0024]FIG. 2 is a timing diagram comparing estimated and actual positionoutputs of a position encoder system;

[0025]FIG. 3 is a timing diagram of a correlated double samplingsequence for a position sampled position transducer;

[0026]FIG. 4 is a timing diagram illustrating the operation of aposition encoder including a QLATCH signal;

[0027]FIG. 5 is a block diagram of a position transducer readheadcircuit;

[0028]FIG. 6 is a block diagram of an interface electronic circuit;

[0029]FIG. 7 is a block diagram of a first embodiment of a highfrequency position estimation circuit that does not use a QLATCH signal;and

[0030]FIG. 8 is a block diagram of a second embodiment of a highfrequency position estimation circuit that utilizes a QLATCH signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031]FIG. 1 is a block diagram of a position encoder 10 and a hostsystem computer or motion controller 30. The terms position encoder andposition encoder system are generally used interchangeably herein,unless otherwise indicated. The position encoder 10 may be any type ofencoder, for example a linear position encoder intended for use by servocontrollers in applications such as pick-and-place machines, fluiddispensing machines, etc. The position encoder 10 includes a scale 12, areadhead 14, a cable 17, and an interface electronics 18. The hostsystem computer or motion controller 30 may be in the form of a servocontroller, and communicates via a cable 20 to the position encoder 10to receive position information.

[0032] In operation, the host system computer or motion controller 30exchanges commands and/or data over the cable 20 with the interfaceelectronics 18. The interface electronics 18 exchanges commands and/ordata via the cable 17 with the readhead 14. In various exemplaryembodiments, the interface electronics 18 may trigger position sampleacquisition in the readhead 14. The readhead 14 collects signals basedon the position of the scale 12 using a readhead transducer element 15,then analyzes and/or digitizes the signals using transducer electronics16, and sends the signals via the cable 17 to the interface electronics18. In various exemplary embodiments according to this invention, theinterface electronics 18 computes position information based on thesignals, and sends the position information to the host system computeror motion controller 30 via the cable 20. As an alternative, in variousexemplary embodiments all or part of the interface electronics 18 may beconfigured as a plug-in card and/or embedded software routines or thelike, and included in the host system computer or motion controller 30.In such cases the cable 20 may be eliminated.

[0033] It should also be appreciated that other types of connectionsbetween the transducer electronics 16 and the interface electronics 18are within the scope of this invention. For example, the readhead 14 mayreceive power from a separate connection (not shown), and the transducerelectronics 16 and the interface electronics 18 may be connected by anynow known or later developed wireless communication methods. In suchcases, the cable 17 may be eliminated. Also, when an application doesnot restrict the volume available in and around the readhead 14, theinterface electronics 18 may be included in or adjacent to the readhead14, and the cable 17 may be eliminated or replaced by any otherappropriate type of connection.

[0034] In various exemplary embodiments, the position encoder 10 andhost system computer or motion controller 30 may operate in a requestand response format, such that the host computer or motion controller 30sends a request for position information and the interface electronics18 responds with the position information. In various exemplaryembodiments according to this invention, the interface electronics 18responds with estimated or approximate position information within aresponse time determined by an operation rate of the interfaceelectronics 18, regardless of an operation rate of the readhead 14. Invarious other exemplary embodiments according to this invention, theinterface electronics 18 continuously outputs estimated or approximateposition information to the host system computer or motion controller30, at a rate determined by an operation rate of the interfaceelectronics 18, regardless of an operation rate of the readhead 14.

[0035] In various exemplary embodiments, the interface electronics 18and readhead 14 may also operate in a request and response format. Thisprocess includes three steps. First, the interface electronics 18 sendsa request for position information. Then, the readhead 14 obtains aposition sample corresponding to an effective sample time. Finally, thereadhead 14 responds by transmitting the position sample information tothe interface electronics 18. In various other exemplary embodimentsaccording to this invention, the readhead 14 operates according to aninternally determined rate and periodically outputs position sampleinformation to the interface electronics 18, at a maximum ratecorresponding to a minimum position sampling and output time, regardlessof an operation rate of the interface electronics 18.

[0036] It should be appreciated that in various embodiments according tothis invention, the effective sample time corresponding to positionsample value determined by the readhead 14 does not correspond to thetime that the position sampling is initiated or the time that theposition sample value is sent to the interface electronics 18. Rather,the effective sample time corresponds to a time point part way throughthe position sampling and output time period of the readhead 14.

[0037] For example, in various exemplary embodiments, the transduceroutput signals are integrated over a period of time (to improve thesignal to noise ratio), and/or the transducer electronics 16 mayimplement symmetric sampling, described further below, so that theposition sample value is based on multiple transducer signal samplesinstead of one. In such a case, the effective sample time corresponds toa time point part way through the position sampling period. An exemplaryembodiment of an encoder utilizing symmetric sampling is described inU.S. Pat. No. 6,304,832, which is commonly assigned and herebyincorporated by reference in its entirety. Various other designconsiderations are related to symmetric sampling and other positionencoder signal processing operations relevant in various exemplaryembodiments according to this invention, including a method forcalibrating a delay time of the effective sample time, which isdescribed in U.S. patent application Ser. No. 10/146,437, which iscommonly assigned and hereby incorporated by reference in its entirety.

[0038] In one embodiment, the position encoder 10 may utilize bothintegration and symmetric sampling and the transducer that is utilizedin the readhead 14 may be an inductive transducer. Various exemplaryembodiments of inductive transducers usable in combination with thisinvention are described in U.S. Pat. Nos. 6,011,389, and 6,005,387,which are commonly assigned and hereby incorporated by reference intheir entireties.

[0039] In accordance with the present invention, an approximatedposition signal may be updated at a rate higher than the base rate ofthe measured transducer position signals. In other words, while thereadhead 14 may provide relatively lower frequency measured transducerposition samples to the interface electronics 18, relatively higherfrequency or on demand output signals representing approximated positionsignals may be being provided to the host system computer or motioncontroller 30. As will be described in more detail below, in oneembodiment the higher frequency or on demand output signals may beprovided by high frequency position estimation circuitry, which may belocated within the system as part of the interface electronics or othercircuitry. As will also be described in more detail below, the highfrequency position estimation circuitry may provide quadrature signalsusable by standard control systems. The high frequency positionestimation circuitry may also be driven by a high speed clock so as torun continuously independent of the sampling process occurring in thetransducer electronics 16. As will also be described in more detailbelow, the accuracy of the system may be further improved by utilizing aQLATCH signal to ensure that the approximated position signal and themeasured position signal that are compared by the error feedback loopcorrespond to the same effective sample time.

[0040]FIG. 2 is a timing diagram illustrating estimated position outputsand actual position information for the position encoder system 10. Aswill be described in more detail below, in accordance with the presentinvention, the estimated position output is updated at a rate higherthan the base position sample rate of the position transducer thatdetermines the measured actual position. As noted above, as compared tothe discrete time interval sampling of the measured transducer actualposition signals from the transducer electronics, in various exemplaryembodiments the estimated position signal may be provided by quadraturegenerating circuitry which is designed to produce relatively continuousquadrature signals throughout the discrete time interval. In general,the measured transducer actual position signals are processed and/orstored by a signal processing circuit at discrete time intervals in aposition register. The estimated position value is generated through thequadrature generating circuitry and is both stored in an output registerand output. Periodically, when a new measured transducer position valueis available, an appropriate estimated position is compared to themeasured transducer position and the resulting difference is stored inan error register for use by the estimated position value circuitryduring the next discrete time interval. As noted above, the utilizationof a QLATCH signal can help ensure that the approximated position signaland the measured position signal that are compared correspond to thesame time.

[0041]FIG. 2 illustrates the interrelationship between the relativelycontinuous estimated position outputs (EPO) of the interface electronics18, the actual position sample values (PSV) determined at discrete timesbased on the signals of the readhead 14, and the underlying continuousactual positions (AP) of the scale 12 relative to the readhead 14. Inthe embodiment shown in FIG. 2, the readhead 14 continuously acquiresposition samples and the related position sample values (PSV) aredetermined, all during a minimum position sampling time P_(sample). Thetime between each time T_(outN) and T_(outN+1) is the minimum positionsampling time P_(sample) in FIG. 2. At a time t_(out1), the estimatedposition output EPO begins to increase at a first rate that isdetermined at the time of an initial adjustment point ADJ-1, as outlinedfurther below. The actual position AP is shown to be increasing fasterthan the estimated position output EPO. During the time interval betweent_(out1), and t_(out2) the readhead 14 acquires position samples and therelated position sample value PSV1 is determined corresponding to aneffective sample time t_(se1). Nominally, the actual position AP is thesame as the position sample value PSV1 at the effective sample timet_(se1), as shown in FIG. 2.

[0042] At a time t_(out2), the rate of change of the estimated positionoutput EPO is adjusted, as indicated by the corresponding adjustmentpoint ADJ-2. The adjustment in the rate of change of the estimatedposition output EPO at the adjustment point ADJ-2 is made at least inpart based on the computation of the difference between the positionsample value PSV1 and the estimated position output EPO at the previouseffective sample time t_(se1) As will be described in more detail below,the use of a synchronizing signal QLATCH at the effective sample timet_(se) can help ensure that the value of the estimated position EPO thatis compared to the position sample value PSV1 corresponds to the sameeffective sample time.

[0043] During the time interval between t_(out2) and t_(out3) thereadhead again acquires position samples and the related position samplevalue PSV2 is determined corresponding to an effective sample timet_(se2). Nominally, the actual position AP is the same as the positionsample value PSV2 at the effective sample time t_(se2). In accordancewith the difference between the estimated position output EPO and theposition sample value PSV2 at the effective sample time t_(se 2), anadjustment in the rate of change of the estimated position output ismade at the output time t_(out3), as indicated by the correspondingadjustment point ADJ-3. Each output time t_(out) is the time that a newposition sample value, such as PSV2 or the like, is available in theinterface electronics 18. Thus, at each output time t_(out) , theinterface electronics 18 has a new basis for determining a new rate ofchange of the estimated position output, as outlined further below. Invarious exemplary embodiments, depending on the operation of thereadhead 14, there may be a time difference between the effective sampletime t_(se) and the output time t_(out) for a position sample value PSV.This time difference is shown as the lag time T_(lag) in FIG. 2. Theoperations of the timing diagram shown in FIG. 2 similarly continue foroutput times t_(out3) to t_(out6), effective sample times t_(se3) tot_(se5), adjustment points ADJ-4 to ADJ-6, and position sample valuesPSV3 to PSV5, with adjustments being made in the rate of change of theestimated position output EPO as the estimated position output EPOsystem follows the position sample values PSV that are nominally theactual position AP at their respective effective sample times.

[0044] It should be appreciated that the operations of the timingdiagram shown in FIG. 2 are representative of operations that continueindefinitely in various exemplary embodiments according to thisinvention. The previous description is for an embodiment where a newrate of change of the estimated position output EPO is based on adifference between the position sample value PSV and the estimatedposition output EPO which both correspond to the previous effectivesample time t_(se). However, it should also be appreciated that invarious other exemplary embodiments, a new rate of change of theestimated position output EPO can be based on a difference between aposition sample value PSV and an estimated position output EPO whichcorrespond to different times within the time interval T_(outN) toT_(outN+1). It should appreciated that this will somewhat degrade theaccuracy of the corresponding estimated position outputs EPO. However,because the time interval T_(outN) to T_(outN+1) may be short relativeto the response frequency of many practical mechanical motion systemsand actuators, the estimated position outputs EPO from such anembodiments may still be adequately accurate for many practicalapplications.

[0045]FIG. 3 is a diagram schematically illustrating an exemplarysymmetric sampling sequence, such as that described in U.S. Pat. No.6,304,832, incorporated above. Symmetric sampling is essentially amethod of sequentially collecting signal samples from multiple positiontransducer signal channels. Briefly, for symmetric sampling, each signalchannel is sampled twice—once at a respective time interval before aneffective synthetic sample time and at the same respective time intervalafter the effective synthetic sample time. Thus, by averaging the twosignal samples it is possible for each transducer signal channel to havethe same effective synthetic sample time, which corresponds to a singletransducer position, such that the multiple signal samples may beproperly combined for determining that position. The effective syntheticsample time of such symmetric sampling methods is one embodiment of theeffective sample time, described above with reference to FIG. 2, that isused in various exemplary embodiments according to this invention.

[0046] Phase signals S1, S2 and S3 are shown in FIG. 3 for one scaletrack of a position encoder. According to the symmetric sampling method,the three signals are sampled over a time T_(s) such that a signal +S₁is sampled during a first sampling interval at an effective sample timethat precedes time t₁ by a preceding offset period PO₁. Similarly, asignal +S₂ is sampled during a second sampling interval, a signal +S₃ issampled during a third sampling interval, a signal −S₃ is sampled duringthe fourth sampling interval, a signal −S₂ is sampled during a fifthsampling interval, and a signal −S₁ is sampled during a sixth samplinginterval. Ideally, PO_(n) equals TO_(n) for these six signals. When allsix signals have been acquired, they are combined into synthetic samplesS′_(n) in the following manner:

S′ ₁=(+S ₁)−(−S ₁)   (Eq. 1)

S′ ₂=(+S ₂)−(−S₂)   (Eq. 2)

S′ ₃=(+S ₃)−(−S ₃)   (Eq. 3)

[0047] This method of combining the six signals into three, results inan averaging effect. If the transducer is in a state of high velocitymotion during the sampling period, the averaging of the signals, asshown above, produces results similar to what would have been obtainedif the six measurements would have been acquired simultaneously at thetime t₁. The time t₁ is taken as the effective synthetic sampling timefor the corresponding position measurement X₁ from the positiontransducer scale. When the three signals S′₁, S′₂, and S′₃ areprocessed, the position X₁ can be determined from these signals with ahigh degree of accuracy, independent of the velocity of motion. Thetimes t₁ and t₂ are similar to the effective sample times t_(se) of FIG.2. As will be described in more detail below, these effective sampletimes t₁ and t₂ may also correspond to a QLATCH synchronizing signal.

[0048]FIG. 4 is a timing diagram illustrating the operation of anexemplary embodiment of the position encoder 10 that utilizes symmetricsampling and a synchronizing QLATCH signal. FIG. 4 shows the timing ofthe signals QLATCH, RQS, and INT. As described in more detail below, thesignal QLATCH is generally generated by the system that generates thecontrol signals for the transducer position samples. The signal QLATCHis generated such that it occurs at the effective sample time t_(se) ofthe transducer sampling sequence, as previously described.

[0049] In various exemplary embodiments the signal RQS may be a positionrequest signal generated by the interface electronics 18. In variousother exemplary embodiments the signal RQS may be a position sampleinitiating signal generated internally by the transducer electronics 16.The signal INT is an internal signal inside the readhead transducerelectronics 16. The position sample process is initiated at a time t₀ bythe reception of the RQS pulse (which is defined as active low), in acircuit of the transducer electronics 16. At a time t_(d) (which is ashort time after time t₀), as indicated by the signal INT going high,the readhead transducer electronics 16 begins to sample the transducersignals. The time delay between the time t₀ and the time t_(d) includesany inherent minimum signal delays and startup periods required for thereadhead 14 to actually start the sample acquisition after receiving theRQS pulse.

[0050] While the signal INT is high, during an integration intervalT_(i1), the readhead transducer electronics front-end reads andintegrates at least one analog transducer output signal. This is thefirst of two similar samples in the symmetric sampling sequence. At atime t₁, the integration of the first sample ends and the readheadtransducer electronics holds the sample for conversion to a digitalvalue. The integration interval T_(i1) may correspond to one or more ofsampling intervals corresponding to the offset periods PO_(n), aspreviously discussed with reference to FIG. 3. At a time t₂, acquisitionof the second sample in the symmetric sampling sequence begins.Integration of the second sample continues for an integration intervalT_(i2). At a time t₃, the integration of the second sample ends and thereadhead transducer electronics holds the second sample for conversionto a digital value. The integration interval T_(i2) may correspond toone or more of the sampling intervals corresponding to the offsetperiods TO_(n), as previously discussed with reference to FIG. 3. Aposition sample value output is available at a time t_(out).

[0051] It should be appreciated that each sampled and held signaleffectively captures the actual transducer position(s) for thecorresponding sample time period. Therefore, these are the respectivetimes and transducer positions which have a relation that is relevant tothe effective sample time. The digital value conversion process has nosuch direct relation to the transducer position. Therefore, the digitalvalue conversion process and associated data transmission is notdiscussed in detail herein as various methods for performing the digitalvalue conversion process and associated data transmission will beapparent to one of ordinary skill in the art.

[0052] As shown in FIG. 4, an effective sample time t_(se) is defined asbeing the median between the end of the first integration intervalT_(i1) and the start of the second integration interval T_(i2). Asdescribed in more detail in the above incorporated 10/146,437application, a desired specification delay time t_(sdspec) is alsoillustrated. With regard to the effective sample time t_(se), using thetimes t₁, and t₂, the effective sample time t_(se) can be calculatedaccording to the following equation: $\begin{matrix}{t_{\quad {s\quad e}} = \frac{t_{1} + t_{2}}{2}} & \left( {{Eq}.\quad 4} \right)\end{matrix}$

[0053] As noted above, in various exemplary embodiments, the effectivesample time t_(se) determines the timing of the QLATCH signal. Invarious exemplary embodiments, the QLATCH signal ensures that theestimated position signal that is compared to the measured positionsample value signal correspond to the same time.

[0054]FIG. 5 is a block diagram of one exemplary embodiment of areadhead 14, including an exemplary transducer electronics 316 and anexemplary readhead transducer element 315. As noted above, the QLATCHsignal may be generated by the circuitry that determines the timing forthe measured transducer signals, and thus the transducer electronics 316may provide the QLATCH signal through the cable 17 to the interfaceelectronics 18. In an alternate embodiment, the high frequency positionestimation circuitry could be contained within the readhead 14, in whichcase the QLATCH signal could be self-contained.

[0055] The readhead transducer element 315 is the readhead portion of a3-track absolute inductive position transducer such as that disclosed inthe incorporated '832 patent. The transducer electronics 316 includestransmitter drivers 310A, 310B, and 310C, each of which receives adigital input signal ENA, ENB, and ENC, respectively, which enable thedrivers. The drivers generate sine-wave signals that are input torespective transmitter windings TXA, TXB, and TXC of the readheadtransducer element 315. Only one driver, corresponding to one track ofthe absolute inductive position transducer, is enabled at one time. Inone embodiment, the sine-wave that is generated by the drivers may be inthe frequency range of 10-16 megahertz, and this sine wave is also usedas the readhead local oscillator which governs readhead operations, asdescribed further below. A respective scale track (not shown) of theinductive position transducer modulates the amplitude of the transmittersignal as a function of position, and a respective set of receiverwindings of the readhead transducer element 315 outputs the modulatedsignal amplitudes on respective sets of receiver pins RA, RB, or RC. Inthe embodiment shown in FIG. 5, each respective set of receiver pinscorresponds to 3 receiver windings, corresponding to one track of theabsolute inductive position transducer.

[0056] The respective sets of receiver pins RA, RB and RC are coupled toan application specific integrated circuit 317. The application specificintegrated circuit 317 multiplexes the signals as needed, and thendemodulates them to determine their respective signal amplitudes. Theapplication specific integrated circuit 317 then amplifies andintegrates the phase signals before they are multiplexed to the outputof the application specific integrated circuit 317. The applicationspecific integrated circuit 317 uses attenuated versions of thetransmitter signals on its inputs SYNC to drive its synchronousdemodulator.

[0057] A complex programmable logic device 322 communicates with theapplication specific integrated circuit 317 over one or more signalconnections 319 and stimulates the application specific integratedcircuit 317 to acquire the samples in a given sequence, then to outputthe samples, one at a time, to a differential analog-to-digitalconverter 320. The differential analog-to-digital converter 320 convertsthe analog signals to digital, and then clocks the data out on a serialport to the complex programmable logic device 322. It should beappreciated that the operations of the application specific integratedcircuit 317 and the differential analog-to-digital converter 320 mayalternatively be combined into a single signal processing circuit thatinputs analog signals from the position transducer element 315 andoutputs corresponding digital data to the complex programmable logicdevice 322. The complex programmable logic device 322 passes the data tothe signal transceiver chip 324, which outputs signals to the interfaceelectronics via the cable 17 or alternative connections as previouslydescribed. The signal connections 319 may also carry various internaltiming signals between the application specific integrated circuit 317and the complex programmable logic device 322. The complex programmablelogic device 322 may in turn relay timing signals to and from the signaltransceiver chip 324. For example, in one exemplary embodiment thecomplex programmable logic device 322 may pass the QLATCH timing signalto the signal transceiver chip 324, which outputs the signal to theinterface electronics 18 via the cable 17 or alternative connections aspreviously described.

[0058] In operation, the complex programmable logic device 322 detectsthe RQS pulse and begins the position sample sequence. The complexprogrammable logic device 322 controls the transmitter drivers 310A,310B, 310C, the application specific integrated circuit 317, and theanalog to digital converter 320, to produce position signal samples in apredetermined sequence.

[0059] The periodic transmitter signals at the outputs of thetransmitter drivers 310A, 310B, and 310C are used as the readhead localoscillator which governs various readhead operations, as disclosed inthe incorporated patents. The signals are converted from analog todigital clock signals by three Schmitt triggers 314. The complexprogrammable logic device 322 is coupled to clock signals from theSchmitt triggers 314 and selects the appropriate clock signal TX0-TX2depending on which driver is enabled. The selected clock is used toclock the state machines inside the complex programmable logic device322. This configuration is designed such that the state machines aregenerally synchronized with the application specific integrated circuit317, so that proper timing can be maintained.

[0060]FIG. 6 is a block diagram of one exemplary embodiment of theinterface electronics 18. The interface electronics 18 is coupled to thehost system computer through a host computer connector 354, whichcarries a power supply for the encoder system and couples communicationsignals to and from one or more line transceivers 352. The linetransceivers 352 provides communication signals at designated voltagelogic levels. In one embodiment, the power supply is a 5 volt supply andthe designated voltage logic levels are 3.3 volts.

[0061] A dual linear voltage regulator 360 provides a required voltage,(in one embodiment 1.8 volts) for the core of a digital signal processor342, as well as a supply voltage (in one embodiment 3.3 volts) forpowering all of the logic devices in the interface electronics,including the signal transceivers 340 and line transceivers 35 . Aswitching power supply 362, which receives a supply voltage from thehost computer connector 354, provides two voltage levels to the cable 17or alternative connections as previously described. In one embodiment,the two voltage levels provided by the switching power supply 362 are10.5 volts and 5.8 volts, which are applied to the cable 17. The cable17 carries power to, and signals to and from the readhead 14 (see FIG.5). The signal transceivers 340 convert the signals over the cable 17 toand from the readhead signal transceiver chip 324 (see FIG. 5) todesignated voltage logic levels. In one embodiment, the designatedvoltage logic levels are 3.3 volts.

[0062] It should be appreciated that in various alternative embodimentswhere the interface electronics is located in or near to the readhead14, the cable 17 and the transceivers 340 and/or the signal transceiverchip 324 (see FIG. 5) may be omitted. It should be appreciated that invarious other embodiments where the signal transceivers 340 send andreceive signals in a wireless configuration, the cable 17 only carriespower to the readhead 14 (see FIG. 5). In yet other embodiments wherethe signal transceivers 340 send and receive signals in a wirelessconfiguration, the readhead 14 is supplied with power separately, andthe cable 17 is eliminated.

[0063] The digital signal processor 342 exchanges commands and/or datawith the host system computer or motion controller 30 (see FIG. 1) viathe host computer connector 354 and the line transceiver 352. Thedigital signal processor 342 may also exchange commands and/or data withthe readhead 14 via the signal transceivers 340 and the cable 17. Thedigital signal processor 342 also receives digitized data from thereadhead 14. In various embodiments, the digital signal processor 342also computes the absolute position based on data from the readhead 14and exchanges position information with a high frequency positionestimation circuit 390 according to this invention, as described furtherbelow. A high speed accurate clock 350 is connected to govern variousoperations of the digital signal processor 342.

[0064] In various embodiments, a flash memory 344 stores the digitalsignal processor 342 program code and transducer calibration data. In analternate embodiment, the flash memory 344 may also store fuse maps fora field programmable gate array 346. The field programmable gate array346 (which is not included in some embodiments) converts serial datafrom the readhead to an appropriate format for the digital signalprocessor 342. The field programmable gate array 346 may provide partialfunctionality of a universal asynchronous receiver-transmitter for hostcommunications, and it may also be used to implement a dynamicallyprogrammable host interface protocol.

[0065] A high frequency position estimation circuit 390 according tothis invention is connected to the digital signal processor 342 and isalso connected to the high speed accurate clock 350, which governsvarious operations of the high frequency position estimation circuit390. The high frequency position estimation circuit 390 in oneembodiment may comprise high frequency quadrature signal generatingcircuitry. As will be described in more detail below with reference toFIG. 7, because the high speed clock runs independently of theoperations of the readhead 14, the high frequency position estimationcircuit 390 runs continuously, independent of and faster than thesampling process occurring in the transducer electronics 16. Thus, thehigh frequency position estimation circuit is able to produce quadratureoutputs that can be utilized by selected types of standard processingcircuitry in the industry, as previously described. As will also bedescribed in more detail below with reference to FIG. 7, the highfrequency position estimation circuit 390 may also include an errorcorrection feedback loop for comparing the measured transducer positionsample value PSV to the corresponding estimated position output EPOgenerated by the high frequency position estimation circuit 390.Furthermore, as will be described in more detail below with reference toFIG. 9, in various embodiments the high frequency position estimationcircuit 390 may also be connected to the signal transceivers 340 and thecable 17 in order to receive a QLATCH signal from the transducer systemreadhead 14, which ensures that the measured position sample value PSVand the estimated position output EPO compared in the error correctionfeedback loop correspond to the same time. When such a QLATCH signal isprovided, the estimated position output EPO can be made relatively moreaccurate.

[0066] As indicated by the dashed outline in FIG. 6, two or more of thedigital signal processor 342, the high frequency position estimationcircuit 390 and the field programmable gate array 346 can be provided bythe circuits and/or operations of a highly integrated digital circuit395. Thus, it should be appreciated that in various exemplaryembodiments according to this invention, at least some of the circuitsand/or operations of the digital signal processor 342, the highfrequency position estimation circuit 390 and the field programmablegate array 346 may be merged and/or indistinguishable.

[0067]FIG. 7 is a block diagram of one embodiment of high frequencyposition estimation circuit 390 that does not utilize a QLATCH signal.As shown in FIG. 7, the digital signal processor 342 and the high speedclock 350 (see FIG. 6) are coupled to the components of the highfrequency position estimation circuit 390 that calculates the absoluteposition every T seconds. The high frequency position estimation circuit390 includes a position register 410, a quadrature counter 420, a QSUMregister 430, an adder 440, a QSPEED register 450, an adder control 460,an error calculator 470, and a digital filter 480.

[0068] In operation, the high frequency position estimation circuit 390inputs a position value from the digital signal processor 342 that isthe most recent position sample value PSV determined based on the mostrecent position samples acquired by the readhead 14. The most recentposition sample value PSV is input to the position register 410. Thequadrature counter 420, in addition to outputting the quadrature signalsQUAD A and B, as outlined below, continuously holds a “real time”accumulated estimated position value based on the operations highfrequency position estimation circuit 390. When a new position samplevalue PSV is input to the position register 410, the error calculator470 inputs the new PSV and the current accumulated estimated positionvalue, and determines the difference between these position values.

[0069] The digital filter 480 acts on the difference determined by theerror calculator 470. The digital filter 480 implements varioustime/frequency filtering parameters and gain factors to achieve bothrapid correction of estimated position errors by high frequency positionestimation circuit 390 and “servo stability” of the high frequencyposition estimation circuit 390. The design and operation of suchdigital filters is commonly known by one skilled in the art of motioncontrol, and may be determined by analysis and/or experiment for aparticular type of transducer readhead and position encoder systemaccording to this invention. Therefore the detailed design of thedigital filter 480 is not described in detail herein.

[0070] In general, difference determined by the error calculator 470will not be zero, that is, the estimated position error will not bezero. The error is acted upon by the digital filter 480, and the outputof the digital filter 480 is the new value to load into the QSPEEDregister 450. In general, a value loaded into the QSPEED register 450governs the rate that the estimated position output changes (aspreviously described with reference to FIG. 2), until the next newposition sample value PSV is determined and input to the positionregister 410 and the previously described operations repeat.

[0071] In general terms, if the quadrature counter 420 value is largerthan the position register 410 value, then the error in the errorcalculator 470 is negative, and the new value loaded into the QSPEEDregister 450 will be reduced from the previous value. This will reducethe quadrature frequency, and then the error will diminish. If theopposite situation is true, and the error is positive, the new valueloaded into the QSPEED register 450 will be larger than the previousone, the quadrature frequency will increase, and then the error willagain diminish in magnitude.

[0072] The QSUM register 430 acts as an integrator register. The valuein the QSPEED register 450 and the value in the QSUM register 430 arecontinuously summed together in an adder 440, and the resulting sum isoutput back into the QSUM register 430. This summing operation occurs ata high frequency determined by the high speed clock 350. Because thesumming frequency is much greater than the frequency at which newposition sample values PSV are available and new values are loaded intothe QSPEED register 450, the summing action can be accurately modeled asan integrator.

[0073] If the QSPEED register 450 contains a positive value, as it iscontinuously summed into the QSUM register 430 at a high rate, the adder440 will periodically overflow due to the increasing value of the QSUMregister 430 and output a carry pulse. The adder control circuit 460will detect the carry pulse, and send a count up pulse to the quadraturecounter register 420. If the QSPEED register 450 contains a negativevalue, as it is continuously summed into the QSUM register 430 at a highrate, the QSUM register 430 will periodically underflow due to thedecreasing value of the QSUM register 430 and output a borrow pulse. Theadder control circuit 460 will detect the borrow pulse, and send a countdown pulse to the quadrature counter register 420.Every time thequadrature counter register 420 receives a count up or a count downpulse, it increments or decrements by one count, and also causes the twooutput bits on signal lines QUADA and QUADB to change by one increment,either up or down. As previously described, the rate at which the countup or count down pulse occurs is controlled by the value loaded in theQSPEED register 450. If the QSPEED register 450 is N bits wide, then thefrequency of the up/down pulses, which is the quadrature countingfrequency, is given by: $\begin{matrix}{{{Quadrature}\quad {Frequency}} = {\frac{QSPEED}{2^{N}}F_{clock}}} & \left( {{Eq}.\quad 5} \right)\end{matrix}$

[0074] where F_(clock) is the frequency of the high speed clock. If N=16for example, then the dynamic range of the quadrature outputs QUAD A andQUAD B is 65,536:1.

[0075] It will be appreciated that because the high speed clock 350 runsindependently of the operations of the readhead 14, the high frequencyposition estimation circuit 390 runs continuously, independent of andfaster than the sampling process occurring in the transducer electronics16. Thus, the high frequency position estimation circuit is able toproduce quadrature outputs that can be utilized by selected types ofstandard processing circuitry in the industry, as previously described.

[0076]FIG. 8 is a block diagram of one embodiment of high frequencyposition estimation circuit 390 that utilizes a QLATCH signal. Theembodiment shown in FIG. 8 includes similar elements and operatessimilarly to the embodiment shown in FIG. 7, unless otherwise indicated.Therefore, only certain elements that require additional explanation aredescribed below.

[0077] In addition to the elements previously described with referenceto FIG. 7, the embodiment shown in FIG. 8 also includes a control signalQLATCH, that is utilized to synchronize the estimated position signal ofthe high frequency position estimation circuit 390 with any new positionsample value PSV that is input to the position register 410 and then tothe error calculator 470. The QLATCH signal is provided from the digitalsignal processor 342 or directly from the readhead 14 through the signaltransceivers 340 (see FIG. 6) to a quadrature latch register 490.

[0078] As described above with reference to FIG. 4, the signal QLATCH istimed so that it occurs at the effective sample time of the readhead 14.Thus, when the signal QLATCH is received by the high frequency positionestimation circuit 390, it causes the quadrature latch register 490 toimmediately record a copy of the accumulated estimated position value inthe quadrature counter 420. The value stored into the quadrature latchregister 490 then corresponds with a high level of accuracy to theposition values determined for the effective sample time correspondingto the generated QLATCH signal. It will be appreciated that the signalQLATCH thus provides a synchronizing link between the two systems, whichare operating at two different rates. Thus, when the error calculator470 and the digital filter 480 operate on values in the quadrature latchregister 490 and the position register 410, there will be little or noerror introduced by effective timing differences and the accuracy of theestimated position values and/or quadrature signals QUAD A and QUAD Boutput by the high frequency position estimation circuit 390 will haveenhanced accuracy relative to those output by the embodiment describedwith reference to FIG. 7.

[0079] While various exemplary embodiments of the invention have beenillustrated and described above, it will be appreciated that variouschanges can be made therein without departing from the spirit and scopeof the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A position monitoringsystem, comprising: a position transducer; a transducer signalprocessing circuit operably connectable to the position transducer; anda position signal generating circuit operably connectable to thetransducer signal processing circuit; wherein: the transducer signalprocessing circuit generates a transducer sample position outputcorresponding to the position of the position transducer, according to atransducer sample position output interval that is not less that aminimum transducer sample position output interval; and the positionsignal generating circuit generates an approximated position outputapproximating the position of the position transducer, according to anapproximated position output cycle interval which is shorter than theminimum transducer sample position output interval; and wherein theapproximated position output is incremented by a prescribed incrementamount during the approximated position output cycle, and the prescribedincrement amount is adjusted when a new transducer sample positionoutput becomes available, and the adjustment is based at least partiallyon a difference between a difference-determining approximated positionoutput and the new transducer sample position.
 2. The positionmonitoring system of claim 1, wherein at least one of the positiontransducer and the transducer signal processing circuit and the positionsignal generating circuit is operably connectable to at least one otherof the position transducer and the transducer signal processing circuitand the position signal generating circuit, through one of a wirelesscommunication interface circuit and a wired connection.
 3. The positionmonitoring system of claim 1, wherein the difference-determiningapproximated position output is selected by one of the transducer signalprocessing circuit and the position signal generating circuit, based ontiming information corresponding to the timing of the new transducersample position.
 4. The position monitoring system of claim 3, whereinthe timing information corresponding to the timing of the new transducersample position is a value-latching signal output by the transducersignal processing circuit and input by the position signal generatingcircuit.
 5. The position monitoring system of claim 3, wherein thetiming information corresponding to the timing of the new transducersample position is one of serially-transmitted timing data andparallel-transmitted timing data, output by the transducer signalprocessing circuit and input by the position signal generating circuit.6. The position monitoring system of claim 1, wherein the transducersample position output interval corresponding to the sample timing ofthe new transducer sample position is determined by one of thetransducer signal processing circuit and the position signal generatingcircuit based on timing information corresponding to the timing of thedifference-determining approximated position output.
 7. The positionmonitoring system of claim 7, wherein the timing informationcorresponding to the timing of the difference-determining approximatedposition output is an approximated position timing signal output by theposition signal generating circuit and input by the transducer signalprocessing circuit.
 8. The position monitoring system of claim 1,wherein the ratio of the nominal approximated position output cycleinterval to the minimum transducer sample position output intervalallows at least 500 approximated position outputs during the minimumpossible transducer sample position output interval.
 9. The positionmonitoring system of claim 8, wherein the ratio of the nominalapproximated position output cycle interval to the minimum possibletransducer sample position output interval allows at least 1800approximated position outputs during the minimum possible transducersample position output interval.
 10. The position monitoring system ofclaim 1, wherein the position transducer comprises an inductive positiontransducer and the approximated position output approximating theposition of the position transducer comprises a quadrature output. 11.The position monitoring system of claim 10, wherein the inductiveposition transducer comprises an absolute inductive position transducer.12. The position monitoring system of claim 10, wherein the transducersignal processing circuit operably connectable to the positiontransducer comprises a symmetric sampling transducer signal processingcircuit.
 13. The position monitoring system of claim 10, wherein theapproximated position output cycle interval corresponds to a maximumquadrature signal frequency, and the maximum quadrature signal frequencyis greater than 500 Kilohertz, corresponding to a quadrature countingfrequency of 2 million counts per second.
 14. The position monitoringsystem of claim 13, wherein the maximum quadrature signal frequency isgreater than 2.5 megahertz, corresponding to a quadrature countingfrequency of 10 million counts per second.
 15. A position monitoringsystem, comprising: a position transducer; a transducer signalprocessing circuit operably connectable to the position transducer; anda position generating circuit operably connectable to the transducersignal processing circuit; wherein: the transducer signal processingcircuit generates a discrete transducer sample position outputcorresponding to the position of the position transducer at a particulartime; the transducer signal processing circuit generates a timinginformation signal corresponding to the particular time; and thetransducer sample position output and the corresponding timinginformation signal corresponding to the particular time are outputtableto the position generating circuit.
 16. The position monitoring systemof claim 15, wherein the corresponding timing information signalcorresponding to the particular time is one of a signal usable tooperate a value-latching circuit, a serially-transmitted timing datasignal and a parallel-transmitted timing data signal.
 17. The positionmonitoring system of claim 15, wherein the corresponding timinginformation signal corresponding to the particular time is output at atime which is not the particular time.
 18. The position monitoringsystem of claim 15, further comprising an approximated positiongenerating circuit that generates an approximated position outputapproximating the position of the position transducer according to anominal approximated position output cycle interval which is shorterthan a minimum transducer sample position output interval of theposition transducer, wherein: the transducer signal processing circuitis operably connected to the position transducer and to the approximatedposition generating circuit; and wherein: the transducer signalprocessing circuit outputs the generated discrete transducer sampleposition output corresponding to the position of the position transducerat a particular time and the generated timing information signalcorresponding to the particular time to the approximated positiongenerating circuit; and the approximated position generating circuitgenerates a first plurality of approximated position outputs that areincremented at a first rate prior to receiving one of the generateddiscrete transducer sample position outputs corresponding to theposition of the position transducer at a particular time and thegenerated timing information signal corresponding to the particulartime; and the approximated position generating circuit generates asecond plurality of approximated position outputs that are incrementedat a second rate after receiving the one of the generated discretetransducer sample position outputs corresponding to the position ofposition transducer at a particular time and the generated timinginformation signal corresponding to the particular time, the second ratebased at least partially on the one of the generated discrete transducersample position outputs corresponding to the position of the positiontransducer at a particular time, the generated timing information signalcorresponding to the particular time, and an approximated positionoutput corresponding to the particular time.
 19. The position monitoringsystem of claim 18, wherein the position generating circuit is remotelylocated from the transducer signal processing circuit.
 20. The positionmonitoring system of claim 18, wherein the position generating circuitcomprises at least a portion of one of a special-purpose custom digitalcircuit, a programmed commercial gate array, a programmed commercialdigital signal processing circuit, a programmed general-purposecomputer, a programmed motion-controller, a general-purpose computer,and a programmed computer used as a motion control system host.